Telephone switching system



Feb. 9 1926. 1,572,222

' w. T. POWELL TELEPHONE SWITCHING SYSTEM Filed March 31 lglg 4Sheets-Sheet 1 INVENTOR WINFRED T POWELL ATTORN EY TELEPHONE SWITCHINGSYSTEM Filed March 31 1919 LKC 4 Sheets-Sheet 2 INVENTOR wmFRED T.POWELL.

ATTORNE Feb. 9 1926. 1,572,222

W. T. POWELL TELEPHONE SWITCHING SYSTEM Filed March 31 3 9 9 4Sheets-Sheet 3 IN'VEENTOR WLHFRED 1-. POWELL M 4! i ATTORNEY Feb. 91926.

W. T. POWELL TELEPHONE SWITCHING SYSTEM Filed March $1 1919 4Sheets-Sheet 4 INVENTOR \NIHFRED T POWELL ATTORNEY Patented Feb. 9, 1926UNITED STATES PATENT OFFICE.

WTNIRED T. PO'WELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROMBERG-CARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK,

A CORPORATION OF NEW YORK.

TELEPHONE SWITCHING SYSTEM.

Application filed March 31, 1919. Serial No. 286,359.

To all whom it may concern:

Be it known that I, VINFRED T. POWELL, a citizen of the United States,residing in Rochester, in the county of Monroe and State of New York,have invented certain now and useful Improvements in Telephone SwitchingSystems, of which the following is a full, clear, concise, and exactdescription.

lVhile my invention is capable of many and varied uses its principalvalue I believe will be in connection with that type of auto matictelephone switching systems wherein a relatively small number ofswitching mechanism units is arranged. For the common use of arelatively larger number of subscribers lines, switching means areprovided to switch a calling line into connection with one of the saidswitching mecha nisms and to isolate the said line and switchingmechanisi'ns from intrusion by other switching mechanisms, or otherlines until the end of the conversational period when the saidswitching; mechanisms may be released from the control of the saidcalling lino, whereupon it will revert tocommon use and may be seized byanother line.

In the systems of the art with which I am aware, it has been the generalpractice to follow one of several courses in construct ing these systemsandv swit'cjhing mechanisms, one course being to make the switchesrelatively large so as to provide an incoming line with possibleconnections to a large number of outgoing lines, Another method consistsin making the system up of a series of switching mechanisms, each beingof relatively smaller size and arranging 'thesc switchingn'iechanisnisso that a first one, commonly called a first selector, maybe operated under a calling substation control to seize asecond, and soon until 2, 8, 4:, or more switching mechanisms are serially connectedto extend a talking circuit between a calling and a called line, itbeing common practice to arrany e these switching mechanisms accordingto the decimal system for convenience in assigning subscribers linenumbers, etc.

lVhile my invention has many objects and secures many advantages, someof which may be employed separately of the others,

it is-a main object of my invention to provide a system in whichrelatively simple switches having movement in one direction only, may beused and in which switches a large number of lines may be reachedwithout the necessity of causing the switch to make an excessive numberof steps.

Another object of my invention is to provide a system in which thestepping of the switches is always in the-same direction, whereby therelease mechanisms for the switches are eliminated together with theconsequent trouble such release mechanisms introduce, such as gettingout of adjustment, wear on the releasing pawls, excessive wear on theswitch bank contacts due to the relatively high speed of the wipers whenreleasing, etc. 1

Other objects of my invention and the invention itself will be apparentfrom a dc scription of two embodiments ofthe same which I haveillustrated in the accompanying drawings in which Fig. 1,- shows oneembodiment wherein the switching system of my invention is illus tratedin connection with what I term a grounded; dial impulse system, and inwhich the switching mechanisms are re turned to normal under the controlof a novel switch restoring controlling means, and in which system otherfeatures of construction and operation as will later appear in thedescription of the same, are contained.

Figs. 2, 3 and lwhen placed together to make one drawing illustrate asecond embodiment ofmy invention wherein the impulse system iscontrolled over the two sides of acalling line in series, and in whichthe rise of the switching mechanisms is ac co. iplished under thecontrol of a pair of interrupters. common to a plurality of suchswitching mechanisms in which other novel features as will hereinafterbe particularly set forth in detail, are disclosed.

Referring to Fig. 1, at A Ishow a calling substation and at B acalledsubstation, line conductors for the calling and called stations beingillustrated connecting the same to a main station at C. At L, 1illustrate a line switch for the calling line which'under the control ofthe calling si'ibsta-tion A is adapted to interconnect circuitconductors of the calling line to circuit conductors of a link circuitLK.

It will be understood that other lines and other link circuits will beprovided for the system, but for simplicity the same have been omittedit being well understood in the art as at this time developed, how suchother lines and link circuits would be arranged in connection with thelines and link circuit specifically illustrated.

In connection with the link circuit LK, I illustrate three switches,each having six contact levels and six wipers simultaneously traversingthe contacts of their respective levels. The wipers lV-1, 2, 1V 8, lV l,lV and VV-6 and the contact banks associated therewith comprise a mastercontrolling or steering switch. Other switches, two of which areillustrated but more of which may be provided in a manner whichwill bemade clear in the description, are shown comprising wipers W7'I to WV12inclusive, designated, a combined register and connector switch, and 43to 18 inclusive, it being understood that the wipers of each switch areadapted all to traverse their respective bank contacts simultaneouslyand it is furthermore understood that all of the wipers illustrated inthe system of Fig. 1 are preferably of the type known as non-bridgingwipers, that is. they preferalily do not make contact with more than oneset of contacts at a time.

Stepping magnets for the master control-' .ling switch and the auxiliaryconnecting switches are shown at SMiif, SMA and SMB respectively. Aplurality of relays for controlling the'operation of these switches bytheir control upon the stepping magnets are illustrated and will be morespecifically referred to in the description of the operation of thesystem which followsz- The subscriber at substation A, upon removing thereceiver to initiate a call, completes an energizing circuit for theline relay LR of the individual rotary line switch L over the: followingpath :-ground G, winding of line relay LR, terminal 1 and wiper 2 ofline switch L, contact 3 of cut off relay CO, line conductor 20, impulsecontact 22 of substation A, transmitter 2?, switch hook contact Ql,induction coil 2', line conductor 21, 'contact 4- ot relay CO, wiper 16and terminal of line switch L and re sistance coil 18 to the source ofcurrent. The

line relay Llt energizes and by closing coir tacts T and 8 places ashunt around con tacts 3 and 4 of relay CO and wipers 2 and 16 of theline switch so that the circuit of the line relay L will notbe openedwhen the cut off relay CO energizes and the wipers leave the hometerminals. The line relay L also closes the following circuit: ground G,contact 5 of relay LR, terminal 26, wiper 1-l and winding .12 of relayCO to the source of current. This ground is also extended to wire 27which leads to the incoming test terminal of this line, therebyimniediately making this line busy to incoming calls.

Relay CO now energizes and closes a circuit from ground G, contact 6 ofline relay LR, terminal 28, wiper 15, contact 10 of relay CO, contact-17 of line switch stepping magnet ST, and winding of magnet ST to thesource of current. This causes the magnet ST to energize, break its owncircuit at contact 17 and retract its armature which moves the wipers 2,1 t, and 16 from the first to the second row of terminals, which secondrow represents-a trunk which will be assumed to be busy and thereforethere will be a ground on terminal 29. This ground will lind a path overwiper 15, contact 11 of relay SO, and winding 13 of relay CO to the entwhich will hold relay .1 its energized position, while ano path may betraced through Contact 7 I o relay CO, contact 17 of magnet ST e windingof ST to the sourceof current. lwiagnct ST will again operate andadvance the wipers to the third row of tern als where the same circuitas traced for Wing the wipers away from the first row of terminals willnow be established to move them to the fourth row. It is to beunderstood that the first third, etc. rows are home or normal points andthe second, fourth, etc., rows are trunk points.

There being no guarding potential on terminals or 31 of the fourth row,this being an idle trunk, magnet ST will not be again. energized andrelay CO will "deenergize. It will be seen that there is a path forwinding 12 of relay GO to the ground G but this path includes two relaywindings and relay CO can be adjusted so as not to hold up through thisresistance. Even if relay CO should hold up it would be for only aninstant because, as will be later described. relay llY will operate andcause magnet SMM to step the wiper lV--2 away from the first terminalwhich opens this circuit to relay GO. Relay CO, upon denergizing,immediately places a guarding potential on this trunk by closing acircuit from ground G contact 9 of relay CO and wiper 15 to terminal 30.Relay CO also, by closing contacts 3 and 4, connects the line conductors20 and 21 to the trunk conductors and 33, and now the closed circuit ofsubstation A on the line establishes the following circuit: ground Gresistance coil 3st, contact 35 of guarding relay GD, contact 36 ofimpulse relay IMP, winding of relay IMP, winding 37 of differentialchange-over relay DC, trunk conductor 32, previously traced closedcircuit of substation A, trunk conductor 33, winding 38 of relay DC,cont-act 39 of relay GD, and winding 1-0 of release relay R to thesource of current. Relays IMP and It energize but DO does not because itis differentially wound. At the same time that the above circuit wasclosed another one was closed as followsz-ground G contact 43 ofauxiliary relay AX, winding 44 of stop relay SP. wiper lV-12- and firstterminal thereof, winding 45 of busy relay BY, wiper lV1l and firstposition thereof, cont-act 46 of brush selecting relay BS, wiper VV2 andfirst position thereof, trunk conductor 47, line switch wiper 14 andterminal 31 thereof and the winding 12 of cut oil relay CO to the sourceof current. Winding-44 of relay SP is low resistance and will notoperate over this circuit but relay BY does energize and closes thefollowing circuit:-ground G winding of master stepping magnet SMll I andcontact 48 thereof, contact 49 of reset relay RS, contact 50 of relayBY, contact 51 of trip relay TP and low resistance coil 52 to the sourceof current. The magnet SMM will now operate and advance the wipers lV-1,V\ 2, lV-3, -4, lV5 and W6 from the first to the second set of.terminals. lViper -2 has now opened the circuit of relay BY whichdeenergizes and off normal contact 53 is opened and 54 closed whichenergizes relay RS over the tollowing circuit :ground G, Winding 55 oirelay RS. contact 54 oi. oft normal springs UV and resistance coil 57tothe source of current. Relay RS looks over the following circuit:ground G contact 58 of relay RS, winding 56 ot relay RS and resistancecoil 57 to the source of current.

The foregoing operations have all occurred in response to the removal ofthe receiver from the hook. The subscriber at substation A may nowoperate the dial in accordance with the first digit of the number of therequired station. When the dial is pulled torward the contact 23 at thesubstation is closed and remains closed until the dial returns to-normaland the contact 22 is opened and closed a number of tunes oorre spendingto the digit selected. Contact 23 places a ground G on both of the lineconductors 20 and 21, this ground on conductor 20 short eircuiting relayLR at line switch L, causing it to deenergize and at the same time shortcireuiting winding 37 of relay DC causing it to become unbalanced and toenergize. Relay IMP, being in series with winding 37 of relay DC, isalso short circuited and deenergized but because relay DC operates, thefollowing circuit is now closed to again operate relay IMP :ground Gcontacts 22 and 23 at substation A, line conductor 20, contact 3o'f'line switch cut oil relay CO, wiper 2, trunk conductor 32, winding37 of relay DC. winding of relay IMP, contact 59 of relay DC, andresistance coil 60 to the source of c1. rent. Relays DC and IMPnow'being energized and their contacts 61 and 36 respectively beingopen,

a short circuit is removed from the winding 42 of relay GD whichenergizes from ground G resistance coil 34, winding 42 ot' relay GD,contact 59 of relay DC and resistance coil 60 to the source of current.Relay GD, energizing removes the short circuit from its winding 41 byopening contact 39, so that this relay will remain in its operatedposition while the circuit including winding 42 is being interrupted byimpulse contact 22 at substation A. The circuit for holding relay GD isas follows :ground G contact 28 of substation A, transmitter 2?, switchhook contact 24, induction coil 2', line conductor 21, contact 4 of lineswitch relay CO, wiper 16, trunk conductor 33, winding 38 of relay DC,winding 41 of relay GD, and winding 40 of relay R to the source ofcurrent. It will be seen that relay DC, upon energizing, closed acircuit from ground G, windings 64 and 68 of relay BS in series, contact62 of relay DC and resistance coil 52 to the source of current, but asthe two.

windings of relay BS are wound dil'l'crentially it will not energize.

The foregoing has all happened as a result of the dial at substation Abeing turned forward and now as it runs baclcthe continuity of the loopis interrupted a number of times at impulse contact 22. As a result ofthese interruptions the line conductor 20, which is connected throughrelay IMP to'the source of current, is opened, thereby causing relay IMPto be deenergized a number of times corresponding to the digit pulled onthe dial. The ground G is not interrupted and therefore relays DC, GDand It will remain energized while these impulses are coming in. At eachdeenergization of relay IMP an impulse is delivered to magnet SMAiWerthe following circuit ground G winding of magnet SMA, wiper -45 andsecond position thereof,- contact 65 of relay GD, coin tact 36 of relayIMP, contact 59 of relay DC and resistance coil 60 to the source otranrent. Magnet SMA will operate at each impulse and step its wipers lV-T,lV-t lV-9, 40, lV-11 and lV12 to a point on their bank corresponding tothe first d'git of the number desired.

Assuming that number 1 was turned on the dial, the magnet 'SMA willadvance its wipers from the first to the second set of terminals andthen the ground G 'at substation A will be disconnected from the lineconductors just before the dial reaches normal. Relay DC will nowagain-becon' e dil terential and release but relays IMP, GD and It willbe held operated over the line. Relay DC, upon deener'giz'ng, closes thefol lowing circuit :-ground G winding and contact 48 of magnet SMM,contact 66 of relay R, wiperlV-10 and second terminal thereof,'contact'67 of relay AX, contact (38 o l relay SP, contact 69- of relayDC and resistance coil 52 to the source of current.

and VV-G to the row of terminals corresponding to the number which wasrecorder on the second switch, as previously described, and as thisnumber was 1 and this second switch .was left on the second row ofterminals, the first switch will be stopped at the first point of thefirst group which is the third set of terminals. The circuit forstoppingthis first switch is as follows :ground G contact 42-3 of relay AX, lowwinding at of relay SP, wiper iv-12 and second terminal thereof, wiper"W 5 and third terminal thereof, wiper lV- and second terminal thereof,contact 67 of relay AX, contact (58' of relay SP, contact 69 of relay DCand the resistance coil 52 to the source of current. This circuit toground G does two things, "first it shunts the mag net SMM so that itwill not aga n energize to move the wipers of the first switch andsecond it will energize relay SP and lock it over thefollowingcircuit:ground G, magnet SMM and contact 48 thereof, contact 66 of relayR, wiper W 10, andsecend terminal thereof, contact 67 of relay AX,winding 70 of relay Si contact 69 of relay DC and r sistancc coil to thesource of current. i

A circuit is now closed from ground G 'wlnding and contact 71 of magnetSMA, contact 72 of relay SF, on normal contact 5 1 and resistance coil57 to th source of current, which circuit causes the second switch toadvance to the eighth set of terminals when wiper \V10 will open winding70 of relay SP, it will deenergize and the second switch will remain onthe eighth set. of terminals. A circu't is now closed from ground GContact elf-l of relay AX, low winding 4% of relay SP, wiper lV i2 andeighth tern'iinal thereof and winding 7?) of relay AX to the source ofcurrent. The winding 44 of relay SP, being of "very low resistance, thisrelay will not be affected but the winding 73 of relay AX, which is ofhigh resistance, will energize relay A X. and lock it frol'i'i'grouml G,make before break contact 75, winding 74;, off normal contact 5% andresistance coil 57 to the source of current. 'telay AX, upon energizing,opens contact 67 which clears wiper li -10 so that it may be used foranother purpose later, and it closes contact 76, the purpose of whichwill .be described later. The subscriber at substation A may now operatethe dial for the second digit but before the results of this operationare described some things will be pointed out in connection with theoper ation of the dial for the first digit.

In'the foregoing description it has been shown that if number 1 is thefirst digit,

the second switch will step to the second'set 'of terminals, establish acircuit by means of its wiper il --12 to cause the first switch to stopon the third set of terminals after which the second switch will hestepped to the eighth set of terminals. It will presently be shown thatas the dial is again pulled forward, relay BS will operate and connectin wipers l V-7 VV8 and lV9 which are the line and test wipers for thelines beginning with digit 1. Now if number 2 was the firstdigit, thesecond switch would step to the third set of terminals, the first switchwould advance to the fourth set of terminals and the second switch wouldhe stepped to the eighth set as before, but this time when the dial waspulled forward for the second digit, relay BS would remain normal whichtime, relay BS will operate and connect in wipers W 18, V-1 l and \V15which are the line and test wipers for the lines beginning with digit 3.lVhen the second digit is sent in from the dial in this case, the thirdswitch will be operated because wiper \V'6 is on the eleventh terminalwhich terminal is connected to the stepping magnet SMB of the thirdswitch. Similarly, if at was the tirst'digit the wipers lV-16, :lV-17and lV18 of the third switch. would be used.

By adding other switches connected to wires 77, 78, 79, 80, S1, 82, and81 iaud connecting in the off normal contacts like ON and (3N othergroups of lines may be served. It will also be noted that correspondingwipers of each switch second, third, etc, are connected together, butthat only one of these switches will be away from normal, or the firstset of terminals, at one time. therefore only one set of wipers will 'beeffective. The numbers of the lines reached on these switches arerepresented by L-11, L-2l, etc.

Returning now to the point where the subscriber.operates the dial forthe second digit, relay .DC operates, as before and, by means of itscontact 59, prepares the impulse circuit for relay IMP. It will beremembered that the first switch was on its third set of terminals andnow relay DC. energizing, closes the following circuit :-groundGiwinding of magnet SMM, and contact 48 thereof, contact 66 of relay R,contact 76'of relay AX, wiper 4 and third'terminal thereof, winding'63 vof relay BS, contact-62 llO of relay DC and resistance coil 52 to thesource of current. This circuit will ener' gize relay BS over itswinding 63, its winding 64 being sufficiently shunted by magnet SMM tounbalance it. If, however, the first switch was on the fourth set ofterminals, because the first digit was 2, the wire 85 connected betweenthe two windings of relay BS would have been open and any currentreceived by one winding would also be received by the other and therelay would not be energized because its windings 63 and (5t are equaland opposite.

Reiay BS will lock, when energized, over the following circuit :groundG", winding 86 of relay BS, contacts 87 and 88 of relay 13 (contacts 87and 88 to make before break contact 89 breaks), contact 54: of offnormal ON and resistance coil 57 to the source of current. Belay BS,upon energizing, closes the follow-in circuit: ground G winding ofmagnet SMli i and contact 48 thereof, contact '66 of relay R, contact 76of relay AX, wiper iV--; and third terminal thereof, contact 88 of relayBS, contact 5% of off normal ON and resistance coil 57 to the source ofcurrent. This causes the first switch to operate and advance its wiperslV1, -2, W-3, ti e, W-5 and lV-6 to the fourth set of terminals fromwhich point they are again advanced by means of the following circuit:ground G5, winding of magnet SMM and contact 4.8 thereof, contact 66 ofrelay R,

contact 76 of relay AX, wiper -4 and fourth terminal thereof, contact 62of relay DC and winding of resistance coil 52 to the sourceof current.If the first switch was on the fourth set of terminals when relay DC opated, this last traced circuit would of c -'irse move it to the fifthset but relay BS would not have been operated. It will be seen that theterminals of A -4 are divided into three groups with the correspondingpoints multipled, therefore the same operations will take place when thethird or fourth switches are used instead of the first.

iitgain returning to the point where the subscriigier o1 crates the dialfor the second digit, (assuming the numb-er dialed to be the impulserelay IMP will deliver five impulses to the stepping magnet for the sec-'ond switch over the following circuit the first swit h atlranced to thefifth set energizes relay TP, but because of the re sistance of TP,magnet SMM will not be energized. Relay TP closes the followingcircuitto energize relay BY :ground G winding of magnet SM and contact 48thereof, contact 66 of relay 1%, contact 76 of relay AX, wiper K -at andfifth terminal thereof, winding 93 of relay BY, contact 94 of relay TPand resistance coil 52 to the source of current. Magnet SMM does not getsufficient current to operate in this case. DC deenergizes as'before, acircuit is closed from ground G winding of magnet SMM and contact 48thereof, contact 66 of relay R, contact 76 of relay AX, wiper W-Jr andfifth terminal thereof, contact 69 of relay DC and resistance coil 52 tothe source of-current, which circuit causes the first switch to advanceits wipers to the sixth set of terminals. This opens the circuit ofrelay TP at wiper -5, TP will deene rgize and, after a short interval,retract its armature, but before its armature restores, the called lineis tested for its busy or idle condition as follows :-if the line isbusy there will either be a ground or anopen circuit on the testterminal on which wiper W9 is resting. (the former if the line had beencalled and the latter if the line had originated a call, its test wire27 being; open at line switch wiper 14c) and if the line is idle a pathto the source of current will be found on the test wire. Therefore ifthe line is busy when relay TP deeneraizes there will be no circuit tohold relay BY, it w ll deenergize and give the calling party the busysignal over the following" circuit ground G common battery, secondaryinduction coil 95 into which a tone is induced, condenser 96, busyinterrupter 97. common busy wire 98. winding; 99 of relay R, contact DC,winding 4.1 of relay GD and Winding Now when the dial stops and relay4.0 of relay R to the source of current.

followt: b and Slfiilli terminal the called line is idle when the stepsits wipers to the sixth set .1 t, a 1 v relay BY will remain energizedover the a circui round G wiper l .*2 thereotl windni'." of

relay ,Y, contact 102 olrclay l7; con

a, 103 of relay BS, wiper il -4), test of called line and called linecut (rcpresented by the ninncral St?) to tu,

source 01'? current. Now when relay 'lP deenergizcs a circuit is closedtroiu ground wind ng" of magnet r thereof, Contact o1 of relay AX, wiperlV-t and sixth terminal thereof, contact fit) of rel of relay T1 2source of cuiTciuQv cut Shir r wipe a switch to the seventh. set i ternrthe following circuit is losed from I a wiper rd sorei contact -i i'called line conductor 104k switch hook Contact 10601 substation ll,condei-ser ringer conductor 105, wiper Y --53, contact 108 and relay BSwiper i -f2 and seventh terminal thereof and resistance coil 3-1 toaround The eli'ect of the resistance coil ill will be to force a smallamount of the. rir 'iug current back through the circuit to suliistationA, thus a" cine the calling part an, indication that c led hell is he; iWhen the called 1 tv removes the rec .iier a direct current 1 1th closedfor the above traced line is led through relays R, GD IMP.

circuit which causes relay T1 to operate and, b means of its contact91-, close a circuit troni ground G. wn ling: a magnet til-EM andcontact 48 thereof. contact 66 of relay Contact 76 oi relay AX, wiperW'al and s. CQDtll tei,"-.- iinal thereof. contact Set of relay T1 andresistance coil to the source oilcnrrent. This operates magnet SMlii andmoves the wipers of the P nrst switch to the eighth or talitmg position.The talking: batte y ted to the called party over the above traced111351111 circuit except that'the battery teed coil Br is substitutedfor the ringing); circuit bymeans of wipers Wl and 1V being on theeighth et of terminals; talking battery for the ca DC and thetwo areconnected together. for voice currents by means of condensers 109 and110.

The calling party releases the connection by hanging up the receiverwhich opens the line and allows relays R, G1) and IMP to dcenergize.Relay R closes the following circuit to energize the cut off relay C0 ofthe line switch L:ground G contact 111 out relay RS, contact 112 ofrelay R, trunk wire lT, terminal 31 and wi or 14: of line switch L, an;yin-ding .2 0t relay CO to "re source of current. The magnet ST of :reline switch is now operated to advance s wipers to the home point fromground contact 113 of relay RS, terminal and ripcr 15 of line switch L,contactlO of re- .a CO, Contact 1'? of magnet ST and the r 'inding ofmagnet ST to the source of ourt It will be noted that this ground G willalso 'keep'this truni-t busy until relay 9 ceenergizes. Another circuitmay now re traced froin'ground G winding of mag- Slilldi andcontact d8thereof, Contact tacts and 54; being switched at each.) A circuit is nowclosed from ground G windmg OfZDflQ'llQt SMA and contact 71 thereof,

contact 116 of otli' normal ON, contact 53 of oil normal ON andresistance coil 57 to the source of current, which will cause the secondswitch to advance its wipers to the ialv point. if the third orv fourthsii'nichcs had been need it can be seen that a corresporuliug operationwould take place" by meansv of oiii' norn'ial ON for thethird s :itch or0H for the TIGOHI' QlL' lVitlrall switches at normal the followingcircuit is closed :ground G contact 58 of relay RS, contact 119 of of?normal 0N contact 118 of off normal ON contact 117 of oil" nor-11ml ON,contact ot oli' normal ON and the resistance coil 5'? to the source ofcurrent i 1 ulnch short circuits winding of relay RS causing ittorelease. Relays A'X and BS are released when contact 5% 0t ofi normal ONis opened, all circuits now being in their normal condition ready foruse again. l'letcrring now to the system of Figs. 2, 3 Piit 4. at 1*; Ishow a calling; substation nstrumen extending interconnecting.

line conductors to a; main station where there is located 2. line switchforthe; line LS,

rrlay contact 115 eta-slay RS,

ted to interconnect conductors of theline circuit of the calling linehaving the substation N, to an idle one of a plurality of link circuitsof which the link circuit conductors LKC are associated with one of thesaid link circuits, other link circuits being provided which areaccessible to the traveling wipers of the line switch LS, but which arenot specifically illustrated. The circuit conductors LKC of the selectedlink circuit are shown extended in Fig. 3, where they terminate incircuits and. apparatus of relays which control the various operationsof a plurality of traveling switch mechanisms illustrated in Fig. 1, therelay controlling means for various switch mechanisms of Fig. at beingillustrated in Fig. 3. A plurality of circuit conductors are shownextending from the relay controlling means of Fig. 3 to the continuationof these circuit conductors leading into the switch mechanisms of Fig.4. A called line substation is illustrated at O in Fig. 1, and the lineconductors leading therefrom to connector switch bank contacts of one ofthe switch mechanisms of Fig. 4 being correspondingly illustrated.

Referrin particularly to Fig. 4c, a plurality of switches each havingone direction of movement is illustrated, the first master controllingswitch having wipers lV2l, W-22, F423 and ll 2 l respectively. A pair ofauxiliary switches operating under the control of the master controllingswitch is illus rated having wipers VV', 7 26, -27, lV-23, VV29, il and431, lV32, lV33, VV3, F435 and EV-36 re spectively. Each of the threeswitches is of the type having a plurality of wipers adapted to besimultaneously moved to simultaneously traverse their associatedcontacts under the propelling actuation of a single stepping magnet, thesame stepping magnet being used to restore the switch to normal bystepping the switch in the same direction in the stepping whichaccompanies the selective function. The stepping magnet for the mastercontrolling switch is illustrated as SliliS, and for the auxiliaryswitches SAS and S138.

It will be understood that in order to increase the number of lineswhich maybe reached by the switching mechanisms of Fig. 1, it would beonly necessary to add the required number of auxiliary switches inaddition to the pair of auxiliary switches illustrated.

In order to convey' a better understanding of the system of my inventionand the invention itself, a description will now be had of the operationof the same.

Upon the removal of the receiver 1* at substation N, Fig. 2, preparatoryto making a call, an energizing circuit is closed for the line relay LLBof line switch LS as follows:-ground G terminal 150, wiper 151, contact152 of cut off relay COR, line conductor 153, induction coil id, switchhook contact 154-, transmitter tr, impulse contact 155, contact 156 ofrelay ch, line conductor 157, contact 158 of relayCOl-Z, wiper 159,terminal 160 and'winding of relay LLB to the source of current. The linerelay LLR when energizing, closes a circuit to cause the line switchwipers 151, 159, 161, 162 and 163 to be advanced from the home point tothe next adjacent row of terminals, which.

is a trunk point, said circuit being as follows: ground G contact 16 1of relay LLB, terminal'166, wiper 161 and winding 167 of relay COR tothe source of current which energizes relay COR'and then ground Gextends through contact 172 of relayLLll, terminal 173, wiper 162,contact 170 of re lay COR, contact 169 of line switch stepping magnetSST and the winding of magnet SST to the source ofcurrent,causing theswitch to advance its wipers to the second row of terminals. If thistrunk is busy there will be a ground on terminal 17 1- which will keeprelay C ll energized and. will cause the magnet SST to again operate,bringing the wipers to the third row of terminals which is another homepoint, from which the wipers will be stepped as from the other homepoint on to the fourth row which represents the idle trunk shown on Fig.3 and Fig. 4:. l'V hen relays LLB and COR operated they closed a holdingcircuit for the line relay LLR by means oftheir contacts 165, 175 and176 so that the line relay LLR would not deenergine when the wipers 151and 159 opencdthe original circuit. When the idle trunk is reachet therewill be no ground potential on terminals 177 and 178, therefore thewipers will come to rest and relays COR and LLB will deenergize. Thisline was innnediately made busy to incoming calls by. the line relay LLRclosing contact 16% and as long as wiper 163 is standing on a trunkpoint,

ground G wiper 163, terminal 18?, 1'36,

etc, will be on the incoming test wire 187. Relay LLB upon deenergizing,opens the battery bridge ofthe line switch at contacts 165 and 175, andrelay OCR, upon deenergizing, extends the line conductors 153 and 157 totrimk'conductors 1841 and 183 respectively. Relay COB. also closes thefollowing circuit to make this seized trunk busy:- ground G wiper 168,terminal 186, con-- tact 171 of relay COR, wiper 162, terminal 177 andtrunk conductor 181. It is of course understood that trunk wires LKC aremulticonductors 18s and 183 may be traced on Fig. 3 to ground G5 atsensitiverelav SN and the sourceof current at marginal relay MG causingthem both energize. It will here be mentioned that relays SN and MG feedtalking battery to the calling party over the above traced circuit andthat condensers 1.90 and 191 are used for the voice current path betweenthe calling and called parties. 1 circuit is also closed from ground Gwiper 163, terminal 186, contact 171 of relay COR, wiper 162, terminal177, trunk conductor 18 1, contact 192 of secondary release relay SR,wire 193, wiper 1V21 and first terminal thereof, contact 203 of thestepping magnet SMS of the first switch and the winding of said magnetto the source of current. This circuit causes mag-net SMS to operate andadvance the wipers W 21, 1V 22, 1V23 and 1V-2l of the first switch tothe second set of terminals.

Relay MG. being energized, now closes a circuit to move the wipers ofthe first switch to the third set of terminals as follows ground Gcontact 209 of relay MG, wire 20st, wiper lV-21 and second positionthere of, contact 203 and winding of magnet SMS to the source ofcurrent.

lhe calling subscriber now operates the calling device, whereby thesubstation im pulse springs 155 are interrupted a number of timescorresponding to the first digit of the called number. Assuming thisnumber to be 1, these springs 155 will send one impulse which will, onthe opening, deenergize relays SN and MG, whereupon HG will close thefollowing circuit :ground G contact 210 of relay MG. wire 205, wiper -21and third terminal thereof, contact 203 and winding of magnet SMS tothesource of current, which advances the wipers of the first switch tothe fourth set of terminals. Just after this opening of contact 155,contact 188 closes which inserts relay ch 11111116 conductor 157, thisrelay will immediately energize and by opening its contact lhfi, willopen the c-ircuitto the impulse contact 155. sistance relay (2000 ohmsfor instance) in the line, marginal relay MG will not energize butsensitive relay SN will energize and cause the first switch to advanceits wipers to the sixth set of terminals over the following circuit:-ground G contact 21].. of olfnormal ON, (off normal contacts ON and ONare associated with thefirst switch and are closed when the wipers areon any but the first set of terminals) contact 213 of relay SN, wiperN21 and its fourth and fifth terminals in turn. contact 203 and windingof magnet SMS to the source of Gli- With this high re-.

and locks over the following circuit:- ground G contact 211 of offnormal ON, contact 216 of relay CHO, winding 217 of relay CH0, andresistance coil 218 to the source of current. A circuit is also closedfrom ground G contact 211 of off normal ON, low resistance coil 221,contact 222 of cut-in. relay Cl, contact 220 of relay CHO, wire 20?,wiper lV21 and sixth terminal thereof, contact 203 and winding of magnetShin to the source of current.which circuit *auses the first switch toadvance its wipers to the seventh set of terminals. Relay CHO closesanother circuit from ground G contact of stop relay STP, wire 202,contact 227 and winding of magnet SAS, wire 201, contact 228 of busytest relay BT, contactof relay CHO, contact 224 of relay ST? andresistance coil 219 to the source of current, which circuit will causethe second switch to advance its wipers to the first set of terminals,assuming that the second switch was left on the second normal pointonthe previous call, (second and third switches 11' re a first normalpoint, first set of terminals. and a second normal point, thirteenth setofterminals) when the following circuit is closed :-ground G contact 230of auxiliary relay A X, low winding 231 of relay STP. contact 232 ofrelay CI, wire 233, wiper il -2e and seventh terli'illltll thereof,wiper 1V3O and first terminal thereof to a point between magnet SAS andthe resistance coil 219 to the source of current. This effectivelyshunts out the magnet SAS, causing it to come to rest and at the sametime energizing relay STP. It

,will be noted that if the second switch was resting on the first set ofterminals (first normal point) when relay CHO operated, the above tracedshunt circuit would have been immediately established which would havecaused relay STP to operate as before but magnet SEAS would not hestepped. lie-- lay ST? will loclr over the following circuit:ground Gcontact 257 of relay AX, contact 255 of relay CHO, contact 258 andwinding of relay STP to the source of current. Before proceeding withthe operation after relay STP energizes, it will now be pointed out whathappens when other numbers such as 2, 3 or 4 are turned on the dia forthe first digi Assuming the calling subscriber to operate the dial fornumber 2, the impulse springs 155 at substation M will be opened andclosed twice, the first opening, as before described, will cause thefirst switch to advance its wipers to the fourth set of terminals.Impulse springs 155 are now closed causing relays 5N and MG to energizeand will again cause the first switch toadvance'its wipers to the sixthset/of terminals. Relay MG'inthisj case being energized, winding 215 orrelay CHO is shunted by ground G contact 211 of off normal ON, lowresistance coil 221, contact 222 of relay CI, contact 246 of relay MG tothe winding 215 of relay CHO, so that CHO will not energize. Thiscircuit from ground G is also traced from contact 246 of relay MG, wire207, wiper -21 and sixth terminal thereof, contact 203 and winding ofmagnet SMS to the source of current, which circuit causes the firstswitch to advance its wipers to the seventh set of tern'iinals. Acircuit is now closed from ground G contact 209 of relay MG, wire 204,wiper lV2l and seventh terminal thereof,'contact 203 and winding ofmagnet SMS to the source of current, which circuit causes the wipers ofthe first switch to be advanced to the eighth'set of terminals. Now whenimpulse contact 155 is opened for the second impulse,'relays SN and MGwill deenergize, and relay MG, by means of contact 210 will step thefirst switch to the ninth set of terminals. Relay oh at substation Nwill now. be energized as before, prevent relay MG from energizing butallowing relay SN to operate and, by means of the previously tracedcircuit through its contact 213, this time cause the first switch tostep to the eleventh set of terminals. A circuit is now closed, asbefore, for energizing the lockingrelay QHO which relay now causes thefirst switch to take another step and go to the twelfth set of terminalswhere the circuit is again closed to cause the second switch to advanceto the second nor mal point (the thirteenth set of terminals) stop thethird switch on its first set of terminals. If 4 was the first digit thefirst switch would have stepped to the twentysecond set of terminals andthe stopping circuit would have been byway of wiper lV-2l, as before,this time through wire 24%) to stop the. third switch on itstl'iirteenth set of terminals which is the second normal point. Thestarting circuit for the magnet SAS of the second switch is by way ofcontact 228 of relay BTas before traced but if either 8 or 4. is thefirst digit, relay Bl will be operated and switch the starting circuitto contact 250 which leads by way of wire 200 to the magnet SBS of thethird switch. Relay ET is energized as wiper w ee passes the. fourteenthand fifteenth termina e the foll g eircuit;-

ground G contact 230 of relay AX, low winding 231 of relay STP, (notaffecting the armature of relay STP) contact 232 of relay CI, wire 233,wiper VV24C and fourteenth and fifteenth terminals thereof, Wire 24%,winding of relay BT and resistance coil 251 to the source of current.Relay BT locks from ground G contact 211' of off normal ON, contact 252of relay BT, winding of relay BT and resistance coil 251 to the sourceof current.

Returning now to the point where relay STP was energized after number 1was turned on the dial at substation N, it will be remembered that thefirst switch was left on the seventh set of terminals and the secondswitch on the first set. Relay CHO, being energizechcloses the followingcircuit :ground G wiper 'VV22 and seventh terminal thereof, wire 236,contact 25a of relay CH0 and winding of relay MG to the scurse ofcurrent, this ground also go- .ing back on truck conductor 183, throughthe line switch LS, line conductor 157 which short circuits relay ch atthe substation N. Relay ch deenergizes, short circuits itself,

relay MG energizes and oloses'a circuit from ground G flco-ntaot 209 ofrelay MG, wire 204e, wiper fi -21 and seventh termi-' nal thereof,contact 203 and winding of mag net SMS' to the source ofcurre'nt, whichcircuit causes the wipers of the first switch to be advanced to theeighth set of termi nals. Relay STP, upon energizing, closes thefollowing circuit to cause the second switch to advance its wipers tothe second setof terminals: ground G contact 230 of relay AX, lowwinding 231 of relay STP, contact 232 of relay CI, wire 233, wiperlV--24 and'sixth, seventh or eighth terminal thereof, wiper 30 and firstterminal thereof,- winding of magnet SAS and contact 227 thereof, wire202, contact 225 of relay STP and resistance coil 219 to the source ofcurrent. It will be seen that if the first digit was 2 this-above tracedcircuit would be by way of wire 24:7, causing the second switch tobestepped to its fourteenth set of terminals, and similar circuits maybetraced for the third" switch when the first digit is :9 O1, :4 V ,7

When the first switch is advanced to th eighth set of terminals, asabove described, a circuit is closed from ground G ,'wiper \V-22 andeighth terminal tl'iereof, wire 238, contact 226 of relay STP, contact256 of relay AX, andresista-nee coil 218 to the source of current, whichgroundshort circuits winding 217 of relay CHO, causmg it to deenergize.Contact 255 of relay CHO now ovens and disconnects the ori inal lockingcircuit of relay STP but relay STP will remain energized and relay AX=will now'energizeoverthe following circuit: ground G coptactflll ofONfQwindin-g giff relay.AX contact 258 and wind-ing%259 or relayysTPr-tothe source of current, which. circuit also holdsrelay STPQThe-subscriber at substation N may now operate the dial for the seconddigit when relays-SN -and MiG-will; functionthe same as before: *Relay-MG, upon. deenergizing, closes acircuit from; ground GFfl-contact 210of relayiMG- wiper W-2l and eighth terminal thereof, contact 203 and-Winding of magnetSMS 'to the. source of current, which circuiteausesthewipers. of the first switch" I to be advanced .to'the ninth setof terminals. A circuit is ;1 1ow-;closedfrom *ground G Wiper W' 22- and:ninthterminal thereof,

Wiper 3V-30 and second terminal thereof, (thistermina l is multiplied tothe other termmal of this secondw switch which follows-nthesecond-normalpoint, and *to corresponding termin-als'of the third switch,

and-isfort-he purpose of causing the proper switch :to be 'steppecl no.inatterwhich normal point it had-1been--set'on,) winding of magnet SASand-contact 227 fthereof, wire 202, contact-2250f relay STP, andresistance coil 219-to the, source? of current, which'circuit causesunagnet'SAS to operate and ad- Vance-the wipers of thensecond switch tothe third set. of .terminals;-' Relay SN,-now= I being energized, willcause the v first switch to advance -rts 'w1pers-pastthe nlnth andtenthsets of -terin'1njalsover the previouslytracedw'circuit; @Theswitchwill be -steppedpast' -wthe eleventh set if relay; 'MG" is energized.Thus it will-the seen that the first witch follows the -iniipulses ofthe dial until" the 'change-oyerpoint is reached when relay hflGremains" deenergized- 'as before described- It will also he seelrtliatfor each impulse, wipeifiVV23 of the first-switch travels over amultiple ;of wire 260 (thiskvireis multiplied to twoterminals and "abridging ibrush: used so as to deliveralong "i'nu uilseto the magnet-SASor SBSg') andin so doing closes a circuit from ground-G contact 211 ofoil normal ON, :c0ntaift' 261 of relay *GHO ,-'wrre 239,

wiperdV-23 and terminal :tliereo f, wire 2G0,

multiple .tern-iinals' and wipe-r -\V-'3O, wind-= ing of magnet SAS,multiple terminals and" wiperi 29, "wire: 195,*'contacts 2G3, and" andresistance coil- 219 to the source of currents-' This circuitr ausesthesecond switch to step *lt'S-Wl1w19' 111"ZICCOlKliUlCQ with: the

nui'nberof impulses-sentinfor the second (llgliigg';

It will be seen+that2-the wire 2t5O"-is con nected to gmultiple;terminals of wiper VV'36 andi -tl1at magnet wSB-S is fconneeted to mu]tipleite-rminal's o f wiper 2VV-35, and if the thirds switch, *insteadofthe second, was

stepped: away hfrom its normal point, these i grounder-impulses=I-throngh-; wipe-r: -23 would he delivered to the magnet Whenthelastdmpulse is sent in from the dial, relay CHO energizes as before andcloses the following r circuit-i ,ground- G winding of secondchangeroyerrelay CV,

contact 255- of relay CHO, contact 258 of relay STP and winding 259 ofrelay STP j to the source of current, which circuit ener-- glzes relayCV. No matter where the wipers of the first switch are resting when thishappens (they may have made more than a completrevolutionor they mayhave made less than a complete revolution depending onthe 'numberfofimpulses sent in r for the second digit,) they will now be advanced tothe twenty-fourth set of terminals, the following circuits to groundbeing found on the different terminals of wiper '1V-21i 1ground G -fromline switch LS 2, 7,12, 17 and 22ground G through contact 209 of relayMG, 3, 8, 13, 18 and be openat contact-2390f relay AX. Relay BT willhowever be operated from ground 29 as wiper V 22 passes the sixteenthterminal. 7

When the wipers of theiirst switch get to the twenty-fourth set ofterminals :1. test is made-of the calleddine as followsz-li said lineisbusythere will'be ground on the :tern'iinal on which wiperWV-QT (or \V33) is resting, placed there either by :1. ternrinat 111g call, aswillbe presently shown, or be cause; the calledlrnefhad originated a'call when this ground wouldhare been placed on the test'terniinal aspreviously described in connection with-wire 187 of Fig. 2. With wiper1V -22on its twentyefourth terminal a circuit is closed from ground Gwiper l -22 and tucnty-foui'fli terminalthereof,

wire 235, contact of relay CV, and re' sist-ance coil .251 to the sourceof current,

saidcircuitshort circui-t-ingrelay RT which 'relayK-beingslow acting,-after 'a short intervalwretrac s-jits armature. The calling part-y'now'hears the busy-signal which is on coinmonwire 266 (placed on wire26% in ':-the same or a similar i'nanneras described for the operationof Fig. 1), by way of condenser 267, Contact 232 of relay "Cl, wire 233,wiper. 2 1 and twenty-fourthlernnnal thereof,w1re.-2-ft0, condenser 191,trunk conductor '184, through the line switch LS and substation N, trunkconductor 183, winch ing of relay 'MG and throughthe battery to, theother side of the bus sfi;induction coil. Disconnection takes place whenthe calli g party hangs up as will be presently described.

Assuming the number dialed to be 41 and this number represented by thesubstation O, the circuit operation after the first switch reaches thetwenty-fourth set of terminals will now be described. Relay BT will beshort circuited as above described but before it releases, a circuitwill be closed from ground G Contact 211 of OH normal ON, contact 213 ofrelay SN, contact 268 of relay CV, winding 269 and contact 270 of relayCI, wire 239, wiper lV-23 and twentyfourth terminal thereof, wire 2 11,contact 271 of relay BT, wire 197, wiper 7-33 (or \V-27 ii": the firstswitch was used) terminal and resistance coil 272 to the source ofcurrent. This circuit energizes relay Cl and, by means of contact 273which makes before contact 270 breakes, it looks from ground G contact211 or off normal ON, resistance coil 221, contact 273 and winding 27-1of relay CI to the source of current. The first switch now advances itsWipers to the twenty-fifth set of terminals over the following circuit,before the armature of relay ET is retracted :ground G contact 211 ofoff normal ON, contact 253 of relay B'l, contact 275 of relay CI, wire 215, and winding of magnet SMS to the source of current, which circuitenergizes magnet SMS and, when relay BT releases and opens contact 253,magnet S-MS deenergizes.

A circuit is now closed formaking the called line busy to other callsand for opcrating the cut off relay of the called .line switch(represented by coil 272) from ground G contact 211 of off normal ON,resistance coil 221, contact 276 of relay CI, wire 197, wiper W33 andterminal thereof and cut off relay 272 to the source of current.

The called partys bellis now rung over the following path: ground Gbattery, re sistance coil 279, generator GEN, interrupter IT, lamp LM,ringing trip relay TRY, wire 243, wiper -2 1 and twenty-fifth terminalthereof, wire 233, contact 277 of relay CI, wire 198. wiper lV32, calledline conductor 280, ringer rg at substation O, condenser on, lineconductor 281, wiper lV-31, wire 199, contact 278 of relay CI, wire 239,wiper il -=23 and twenty-fifth terminal thereof to ground ti hen thecalled party answers a direct current path is closed which energizesrelay TRP, closing the following circuit: ground Or, contact 280 ofrelay TRP, to the winding of relay AX short circuiting AX whichdeenergizes. This ground G also goes through contact 2535 of relay CHOto the windingof relay CV, short circuiting it, causing it to deenergizeand the short circuit is now maintained for relays AK and CV by ground iand conln l 257 of rel y AX, so that when relay TRIP deenergizes neitherof these relays AX and CV, will again energize. Relay CV, upondeenergizing, closes a circuit from ground G contact 211 of oil normalON, contact 213 of relay 2N, contact 281 of relay. CV, wire 208, wiper-21 and twenty-fifth terminal thereof, contact 203 and winding of magnet@MS to the source of current, which circuit causes the first switch tooperate and advance its wipers to the twenty-sixth set of terminals. Thetalking battery is now fed to the called party from ground G winding 282of battery feed coil BF, wire 2 10, wiper W 23 and twenty-sixth terminalthereof, wire 239, contact 278 of relay CI, wire 199, wiper W-31 andte-ii'ininal thereof, called line conductor 281, through the usualsubstation apparatus O, line conductor 280, wiper lV32 and terminalthereof, wire198, contact 277 of relay CI, wire 233, wiper lV-24l andtwenty-sixth terminal thereof, wire 242, and winding 283 of coil BF tothe source of current. The wires leading into coil BF are connected tocondensers 190 and 191 which condensers are also connected to thecalling line as previously described. The talking .circuit is nowestablished between the calling and called parties.

The release of the connection will now be described. The calling party,hanging up the receiver, causes relays SN and MG to be deenergizeol' andthe following circuit closed by relay SN: ground G contact- 211 of oilnormal ON, contact 21% of relay SN, contact 212 of off normal ON,winding o't primary release relay PR, contact 28% of relay PH, commoninterrupter contact 296, and resistance coil 295 to the source ofcurrent, which circuit energizes relay PH andloclzs it with batterythrough resistance coil 286 and con tact 285. Relay PR could beenergized over the above circuit during the time that relay SN wasdeenergized as the impulses were being sent, but-tho circuit wouldbe'again opened, allowing relay PR to deenergize, when relay SN wasenergized. In this case however, relay SN will remain deenergized v forasufficient time to allow the common interrupt-er contact 297 to extendground by way of contact 287 of relay PR, contact 290 and winding 294,01 secondary release relay SR to the source of current. Relay SR willenergize and lock lroin ground. (i contact 211 or ofi' normal ON,contact; 291 and winding 29st to the source of current, this loci;- ingcircuit holding relay SE in its ()Ptltllt-(l position until the firstswitch restores to normal when, by the opening of otl normal contact211, the current will be disconnect cd from winding 294. A circuit isnow closed from this oft normal ground G? and contact 292 of relay SR byway of wire196, wiper lV28 and all off normal terminals thereof, windingand Multan-11227 .ot m gnet SAS,

wire 202, contact'225 of relay STP, and rcsistance coil 219 'to thesource of current,

normal point. It the third switch was the one used instead of thesecond, this ground would go through wiper \V28 and normal (first orthirteenth) terminal thereof, wiper \V34: and all off normal terminalsthereof, Winding and contact 23 1 of magnet SBS, wire 202, contact 225of relay STP, and resistance coil 219 to the source of current, whichcircuit would cause the wipers of the third switch to he stepped totheir normal point. above traced path from ground by way of the normalterminal of wiper 1V3t, contact 203 and winding of magnet SMS to thesource of current,-which circuit causes the Wipers of the first switchto be advanced to its first set of terminals when off normal contacts211 and 212 open 'and break the stepping circuit for the first magnetand the locking circuit for all relays. Relay SR, by

opening contact 298, releases relay CI which deenergizes and keeps theline wipers -25 and 1V-26 or lV-31 andld -32 clear while they arestepped over terminals of lines which may be in use.

The line switch LS is released fron' ground G low winding293 of relaySR,-

contact 289 of relay SR, trunk conductor 182, line switch terminal 17 8,wiper 161 and -winding 167 of line switch cut oft relay COR to thesource of current, thereby energizing relay COR which in turn closes acircuit from ground G low winding 293 of relay SR, contact 288 ofrelay-SR, trunk conductor 181, line switch terminal 177, wiper 162,contact 170 of relay COR, contact 169 and winding of magnet SST to thesource of current. The line switch wipers are now given one step whichtakes them to a home point and, by opening the circuits of line switchterminals 177 and'17-8, relay SR is deenergized. The circuits are now innormal condition ready to again be used.

It will be understood that whereas I-have illustrated specificembodiments of my invention, that the same is capable of being embodiedin systems varying widely "111 ,struc-' tural details from thatspecifically illus trated and described, but what I claim is myinvention is defined in the following cl a nus 2- v 1. In anelectromechanical telephone switching system, the combination with amain station trunk circuit, of a telephone line adapted to beconnectedthereto, of a telephone substation for the said line, a sendingdevice at the said substation, switching mechanism for the said trunkcircuit under.

the control of the saidsending device, the

said switching mechanism comprising a plurality of switches, one of thesaid switches w A circuit is now closed over this 'being'a steeringswitchand another of the said switches being a combined register andconnector switch, means to operate the substation sender to give thesaid combination switch a predetermined setting in accordancewith thefirst digit of the called line number, means responsive thereto, tocause the said steering switch to take a setting cor-' responding to thesetting of the said combination switch, means operative after the saidsetting of the steering switch to cause the said combination switch toalways take a second setting which is the same for every case beingindependent of the first position setting of the said combinationswitch, and means responsive to the second operation of the saidsubstation dial to operate the said ing device at the said substation,switching mechanism for the said trunk circuit under, the control of thesaid sending device, the

said switching mechanism comprising a plurality of switches, one of thesaid switches being a steering switch and another of the said'switchesbeing a combined register and connector switch, means to operate the substation sender to give the said combination switch a predeterminedsetting in accordance with the first digit of the called line number,means responsive thereto, to cause the said steering switch .to take asetting corresponding to thesetting of the said combination switch,means operative after .the said setting of the steering switch to causethe said combination switch to always take a second setting which is-thesame for every 7 case bei independent of the first position setting otthe said combination switch, a plurality of other connector switches,means responsive to the saidsetting of the said steering switch toselect a given one of the said other connector switches or the saidcombination switch, and means responsive to the second action of thesubstation sender to cause the said selected switch to operate to makeconnection with the terminals of the desired called line. i

3. In an electromechanical telephone switching system, thecombination,with a main station trunk circuit, of? a telephone .lineadapted to be connected thereto, ofa telephonesubstation for the saidline, a sending device at the said substation, switching mechanisnrforthe said trunk circuit under the control of the'said sending device, thesaid switching mechanism comprising a plurality of switches, oneof thesaid switches being a steering switch and auother of the telephoneswitching system, the combination with aof the said combination switch,a pluralityof other connector switches, means responsive to the saidsetting of the said steering switcn to select a given one of the saidother conneitor switches or the said combination switch, meansresponsive to the second action of the substation sender to cause thesaid selected switch to operate to make con-.

nection with the terminals of the desired called line, a plurality ofbrush sets on each of the said switches, and a relay responsive to thesetting of the said steering switch to determine which brush set of theselected switch shall be used to make connection with the terminals ofthe desired called. line.

4-. In an electromechanical telephone switching system, the combinationwith a main stationtrunk circuit, of a telephone line adapted to beconnected thereto, of a telephone substation for the said line, asending device at the said substation, switching mechanism for the saidtrunk circuit under the wntrol of the said sending device, the saidswitching mechanism comprising a plurality of switches, one of the saidswitches being a steering switch and another of the said switches beinga combined register and connector switch, means to operate the sub- "ionsender to give the said combination ,h a predetermii'ied setting inaccordance with the first digit of the called line number, meansresponsive thereto, to cause the said steering switch to take a settingcorresponding to the set-ting of the said combination switch, meansoperative after the said setting ot' the steering switch to cause thesaid combination switch to always take a second setting which is thesame for every case being independent of the first position setting ofthe said combination switch, and means responsive to the secondoperation of the said substation dial to operate the said combinationswitch to cause it to make connection with the terminals of the desiredcalled line, a plurality of brush sets for the said combination switch,only one of which is used to make the above desired con-- nection withthe called line, and relay means responsive to the said steering switchsetting to select a particular brush set to make connection with thedesired called line.

5. In a telephone system, the combina' tion with a-telephone line, aplurality of central oflicc trunk circuits, at line switch for the saidline adapted when the said line is a calling line, to interconnect thesaid line with an idle one of the said link circuits, a line relay forthe said line switch, substation apparatus for the said line\ meansunder the control of the said substation apparatus to operate the saidline relay, means under thecontrol of the said line relay tooperate thesaid line switch, normal circuit connections from the line conductors ofthe said line to thesaid line relay, substitute circuit conductors forconnecting the said line relay to the said line conductors when the saidswitch is operating, the said substitute conductors comprising normallyopen contacts of the said line relay, substation apparatus to disablethe said line relay, whereby the said line re-v lay is operativelydissociated from the telephone line conductors by the rupture of thesaid normally opencontacts. I y

6. In a telephone system, the combination with a telephone line,substation apparatus for the said line comprising a sub station sendingdevice, an idle trunk circuit, a line switch for the said line adaptedto make connection with the said idle trunk circuit, switchingmeans inthe said trunk circuit under the control of the said send ing device, aline relay controlling the said line switch, substation apparatusadapted to operate the said line relay when the said line is a callingline, normal connections for the said line relay to the said linecomprising normal contacts of the said line switch, secondary circuitconnections to connect the said line relay with the said line conductorswhen the said switch is operated, the said secondary circuit connectionscomprising normally open contacts of the said line relay, which contactsare closed when the said relay is operated, and disabling means for thesaid .line relay under the control of the said sending device.

7. In a telephone system, the combination with a telephone line,substation apparatus for the said line comprising a substation sendingdevice, an idle trunk circuit, a line switch for the said line adaptedto make connection with the said idle trunk circuit,

as v

switching means in the said trunk circuit under the control of the saidsending device, a line relay controlling the said line switch,substation apparatus adapted to operate the said line relay when thesaid line is a calling line, normal connections for the said line relayto the said line comprising normal contacts of the said line switch,secondary circuit connections to connect the said line relay with thesaid line conductors when the said switch is operated, the saidsecondary circuit connections comprising normally open 'con'tactsot thesaid line re- .lay, which'contacts are close drwhen-the said relay isoperated disabling means for the said.:line relay :under the control ofthe "said sending 'device,the said disabling means operating to disablethe'said' line relay to rupture the said SBQOIldiLIjZgOOIHlBCtlOIlS whent-liexsendin x device is operated to control 1 I l the said switchingineans.

8, In a telephone system, an incoming ci'rcuit, inulti-brush automaticswitch- ".glnd-lylCll la l to isaidf incoming ClICult, a

pluralityf of outgoing circuits arranged in groups iterminating in saidautomatic switch, a'set of brushes on said switch for each group ofoutgoing clrcuits terminating .the eat, -I11G&1IS .IO1 moving all ofsaid'sets' of brushes into/successive engagement with the terminalsof;said'outgoing circuits, means including a progressively 'movableswitch '.associated with said nulti-brnsh switch for controllin g'theoperation" of said automatic. switchjand means including saidprogressively movable switch for selectively rendering one orianother ofsaid sets of brushes effective to connect said incoming.

circuit to a 'wanted foutgoing circuit.

In a telephone" system, an incoming circuit, a plurality of automatic,sw tches individual to said incoming circuit, groups of loutgoing'circuitsterminating in each of {said automatic switches, each automaticswitch being provided. with a, set of brushes for ea'ch egroupofoutgoing circuitsterimi -a i gf t er at, m ns? nclu ng a p gressivelymovable switch n'dividu'al to said .incomingcircuitfor rendering;effective one or another of said jaut-omatic' switches to select a groupof trunks, and means 'includ ing said PIQgI SSIVBb IIIOVablGSwltch for,rendering effective 'aset of brushes off the said incoming selectedswitch for extending circuit of the circuit to awanted outgoing selectedgroup. I

10; In, a telephone system, a subscribers telephone line, a plurality oftrunk lines, a non-numerical switch for extending said subscribers-lineto an idle trunk line on the initiation of acall, a plurality of struc'turally independent switches individual to each trunk, groups ofoutgoing circuits terminating in each of said automatic switches, meansincluding a progressively movable switch individual to a selected trunkfor rendering one or more of said automatic progressively movable switchassociated with said incoming circuit and means includingsaid'automaticswitch for variably setting said progressively movable switch inaccordance with its own ad ustment, and

means including said progressively movable switch for selectivelyrendering effective one of said setsof brushes of said automatic switchfor connecting said incoming circuit a to a wanted outgoing circuit.

In testimony whereof, I. hereunto subscribe my name'thisf29th day ofMarch A. D. 1919.

A WVI'NFRED T. POWELL.

